In a facility where radiation dose is above a reference value and it is difficult to enter the inside, the acquisition of the information inside the facility is sometimes required.
The required information is, e.g., information on physical quantities such as pressure and temperature in the facility or the level of liquid accumulated in the facility.
The physical quantities to be detected are often detected in the form of voltage with the use of a detector.
The transmission mode of the detected voltage is roughly divided into a mode of transmitting the voltage without any conversion and a mode of transmitting the current converted from the voltage by V/I conversion.
The mode of transmitting information in the form of current has a feature that the influence of noise is smaller than the mode of transmitting information as voltage when the transmission distance is long.
In a measuring device that detects and measures such a physical quantity, an indication value to be displayed sometimes deviates from the true value due to, e.g., change in the elasticity of springs inside the measuring device, which is caused by long-term use.
For this reason, in general, the calibration of the indicated value is performed at a specific time, such as at the time of the installation of the detector or every predetermined period after the installation.
Two types of calibration, i.e., the zero point calibration and the span calibration are often performed.
The zero point calibration is such a calibration that the indicated value is caused to become zero when the voltage input into a V/I conversion element is zero.
Hereinafter, the term “zero point current” is used for the amount of an electric current that is outputted from the V/I conversion element when the voltage inputted into the V/I conversion element is zero.
The span calibration is such a calibration that the indicated value is caused to indicate the true value of the physical quantity at each input voltage when plural known voltages are inputted to the V/I conversion element.
Hereinafter, the term “span shift amount” is used for the amount of the deviation of the electric current value outputted by the V/I conversion element from the true value with respect to the inputted known voltage.